There has been disclosed a conventional wavelength multiplexing optical transmission system which, in addition to operational transmission and reception transponders which are used for normal signal transmission, includes reserve transmission and reception transponders which construct a reserve transmission line when a failure occurs in this operational transmission transponder (for example, refer to patent reference 1). Because even when a failure occurs in an operational transmission transponder, the conventional wavelength multiplexing optical transmission system can thus transmit the same signal by using the reserve transponders, instead of this operational transmission transponder, the failure can be sidestepped and the signal transmission can be ensured.